A conventional light scattering type smoke sensor basically includes a smoke chamber through which smoke enters into the sensor from outside. An inside space of the smoke chamber functions as a smoke-sensing space, in which light emitted by a light-emitting element is scattered by smoke, and scattered light is received by a light-receiving element so that occurrence of fire can be detected.
The smoke-sensing space is provided inside the smoke chamber of the sensor in order to realize an accurate sensing of minute scattering light generated by reflection of light by the smoke without being affected by outside light, and also to prevent entrance of foreign substances into the smoke-sensing space. Presence of foreign substances such as a small insect in the smoke-sensing space may cause scattering of light and lead to false alarm. Therefore, the arrangement of the smoke-sensing space inside the smoke chamber is an essential part of the conventional light scattering type smoke sensor (see, for example, Patent Document 1 and Patent Document 2).
Patent Document 1: Japanese Patent Application Laid-Open No. H6-109631 Publication
Patent Document 2: Japanese Patent Application Laid-Open No. H7-12724 Publication